It's the first time the governor acknowledged serious worries about the structural integrity of the $6.4 billion infrastructure project to build a new eastern span of the bridge. Brown had dismissed concerns about broken bolts earlier this month.

Now, the governor said the state is reviewing construction documents going back as far as the administration of former Gov. Gray Davis, who served from 1999 to 2003.

"It's a pretty big issue," Brown told reporters before delivering a graduation speech for University of California, Berkeley political science students. "I drive across that bridge, too."

The new bridge is replacing a span damaged during the 1989 Loma Prieta earthquake. It's already years late and billions of dollars over budget.

State transportation officials recently disclosed that nearly three dozen seismic safety bolts on the eastern span of the bridge had broken. The bolts, or rods, each 17- to 24-feet long, connect the bridge deck to so-called shear keys, which are large shock absorbers that control movement during an earthquake.

"I take it very seriously, and that thing's not going to open unless it's ready," Brown said Monday. "And the engineers are telling me that they're doing the kind of work that will be needed for that."

Just three months ago, Brown had participated in an event to count down the bridge's opening.